USB drives won’t boot

Someone had said “I have a USB drive with a FAT16 file system on it and it won’t boot .”  (But may boot fine on an  older computer) “Windows sees the drive just fine, but the Dumb computer just won’t boot it.”
 This has been a head ache of mine for ever. Some USB drives work some don’t.   Here is my best answer. (for now)

If the USB drive was fdisk/formatted from an older DOS system chances are that it won’t boot on most newer computer. It seems like a lot of BIOS drivers in newer computers rejects the old disk standard FAT 12/16 system where it would start the partition close to the first sector on the drive.  (start at sector 63 was typical) It appears that newer computer BIOS wants the USB drive to start at sector 2048 typical. “Rufus” makes the USB drive with the start sector at the 2048 sector offset and they will boot just fine.

3 different file systems FAT, NTFS, ext2 for DOS, Windows, linux in that order. But things get complicated.  Some older windows will run and do most every thing using a FAT file system, but DOS will not work in a NTFS system. Ext2 is pretty much a linux file system (not DOS or Windows) but aso works with Unix, Zenix, and Minix. There are 3 FAT system, FAT12, FAT16, FAT32. DOS files that work in FAT12 will also work in FAT16 and visa versa. DOS file systems for FAT32 may not wok in FAT12 or 16. Then the is a thing called VFAT a sub branch of FAT16/32. Okay I thing you get the idea. back to simple. A FAT 12 file system can support up to 4077 clusters. A cluster can be 1 to 4 sectors.   Microsoft has put a limit of 8 MB size. A FAT 16 file system can support up to 65,536 clusters.  Microsoft has put a limit of 2TB size, using  64 sector per clusters. A FAT 32 has a limit of 4 TB. The old DOS fdisk/format file system would give you a FAT 12 system for any thing 8 MB or under, a FAT16 for any thing 2.GB or under, a FAT32 for any thing 2.TB or under. How ever these numbers are not cut in stone. Notice that “Rufus” extents the FAT 16 table size up to 8 GB by making the cluster size even bigger. on the other hand a programer could just make all size drive FAT32. Sounds good so Why not? In general a small file systems would suffer severely. The cluster size would be to big, so there would be to few clusters and you would run out clusters and you would not be able to add more files to the file system. (out of disk space error) Also

Someone had said “I have a USB drive with a FAT16 file system on it and I want just boot it no matter what”  If your computer will not boot your USB drive blame your BIOS drivers not your windows OS system. You could open and use the USB drve if you have a floppy drive and an Msdos disk with FAT16, but you don’t. A  bootable CD can be made with Msdos/Freedos and with some USB drivers on it. Msdos/FreeDOS will then mount up to four USB drives and up to four CD ROMs.   I will have a ISO file for the CD soon I hope.

Stick to the FAT32 file system if you can. but some times only a fat12/16 will work. I have recovered some what appeared to be a dead USB drives by reformating them as FAT16. Using the CD.  Windows will then see the USB drive, you then can reformat the drive as FAT32 or what ever. instructs on the CD. More later.